Bucket assembly for turbomachine

ABSTRACT

Bucket assemblies are provided. The bucket assembly includes a shank, and an airfoil positioned radially outward of the shank. The bucket assembly further includes a main cooling circuit defined in the airfoil and the shank, the main cooling circuit comprising seven passages, each of the seven passages fluidly connected with an adjacent one of the seven passages. A maximum rotation number in each of the seven passages is less than or equal to approximately 0.4.

FIELD OF THE INVENTION

The present disclosure relates in general to turbomachines, and more particularly to bucket assemblies in turbomachines.

BACKGROUND OF THE INVENTION

Gas turbine systems are one example of turbomachines widely utilized in fields such as power generation. A conventional gas turbine system includes a compressor section, a combustor section, and a turbine section. During operation of the gas turbine system, various components in the system are subjected to high temperature flows, which can cause the components to fail. Since higher temperature flows generally result in increased performance, efficiency, and power output of the gas turbine system, the components that are subjected to high temperature flows should be cooled to allow the gas turbine system to operate at increased temperatures.

Many system requirements should be met for each stage of the turbine section, or hot gas path section, of a gas turbine system in order to meet design goals including overall improved efficiency and airfoil loading. Particularly, the buckets of the various stages of the turbine section should meet the operating requirements for that particular stage and also meet requirements for bucket cooling area and wall thickness. Internal cooling requirements should be optimized, necessitating a unique internal core profile to meet stage performance requirements enabling the turbine to operate in a safe, efficient and smooth manner.

More specifically, one current trend in bucket design is to increase the maximum thickness (between the pressure side and suction side) of the bucket airfoil, in order to improve aerodynamic efficiency. Further, reductions in airfoil wall and rib thicknesses (between the various cooling passages defined therein) have been encouraged, in order to minimize the overall weight of the bucket. The combination of these two trends, however, has resulted in large cooling passages with large aspect ratios, requiring increased cooling flows therethrough to provide the required convection coefficient for adequate cooling thereof. The present inventors have discovered that, as a result of these trends, the Mach number of the cooling flow through the cooling passages is lowered, leading to increased coriolis effects in the cooling passages. For each cooling passage, this results in uneven cooling, with an increase in the heat transfer coefficient on one of the pressure side or suction side of the passage and a decrease in the heat transfer coefficient on the other side. As a result, cooling of these buckets may be inefficient and non-uniform, and may lead to bucket damage.

Accordingly, improved buckets are desired in the art. In particular, buckets having improved cooling circuits that provide more efficient and well distributed cooling would be advantageous.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In one embodiment, a bucket assembly is disclosed. The bucket assembly includes a shank, and an airfoil positioned radially outward of the shank. The bucket assembly further includes a main cooling circuit defined in the airfoil and the shank, the main cooling circuit comprising seven passages, each of the seven passages fluidly connected with an adjacent one of the seven passages. A maximum rotation number in each of the seven passages is less than or equal to approximately 0.4.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a schematic illustration of a gas turbine system;

FIG. 2 is a sectional side view of the turbine section of a gas turbine system according to one embodiment of the present disclosure;

FIG. 3 is a perspective view of a bucket assembly according to one embodiment of the present disclosure;

FIG. 4 is a front view illustrating the internal components of a bucket assembly according to one embodiment of the present disclosure; and

FIG. 5 is a top view illustrating various internal components of a bucket assembly according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 is a schematic diagram of a turbomachine, which in the embodiment shown is a gas turbine system 10. The system 10 may include a compressor section 12, a combustor section 14, and a turbine section 16. The compressor section 12 and turbine section 16 may be coupled by a shaft 18. The shaft 18 may be a single shaft or a plurality of shaft segments coupled together to form shaft 18. An inlet section 19 may provide an air flow to the compressor section 12, and exhaust gases may be exhausted from the turbine section 16 through an exhaust section 20 and exhausted and/or utilized in the system 10 or other suitable system.

The turbine section 16 may include a plurality of turbine stages. For example, in one embodiment, the turbine section 16 may have three stages, as shown in FIG. 2. For example, a first stage of the turbine 16 may include a plurality of circumferentially spaced nozzles 21 and buckets 22. The nozzles 21 may be disposed and fixed circumferentially about the shaft 18. The buckets 22 may be disposed circumferentially about the shaft 18 and coupled to the shaft 18. A second stage of the turbine section 16 may include a plurality of circumferentially spaced nozzles 23 and buckets 24. The nozzles 23 may be disposed and fixed circumferentially about the shaft 18. The buckets 24 may be disposed circumferentially about the shaft 18 and coupled to the shaft 18. A third stage of the turbine section 16 may include a plurality of circumferentially spaced nozzles 25 and buckets 26. The nozzles 25 may be disposed and fixed circumferentially about the shaft 18. The buckets 26 may be disposed circumferentially about the shaft 18 and coupled to the shaft 18. The various stages of the turbine section 16 may be disposed in the turbine 16 in the path of hot gas flow 28. It should be understood that the turbine section 16 is not limited to three stages, but rather that any number of stages are within the scope and spirit of the present disclosure.

Each of the buckets 22, 24, 26 may comprise a bucket assembly 30, as shown in FIGS. 3 through 5. In exemplary embodiments, the bucket assembly 30 according to the present disclosure is a first stage bucket 22, although in alternative embodiments the bucket assembly 30 may be any suitable bucket. The bucket assembly 30 may generally include a shank 32 and an airfoil 34. The airfoil 34 may be positioned and extend radially outward of the shank 32. Additionally, the bucket assembly 30 may include a platform 36. The platform 36 may be positioned radially between, and may further surround one or both of, the shank 32 and/or airfoil 34. Further, the bucket assembly 30 may include a dovetail 38. The dovetail 38 may extend radially inward from the shank 32, and in some embodiments be a radially inward portion of the shank 32. The dovetail 38 may be configured for coupling the bucket assembly 30 to a rotor wheel (not shown).

The airfoil 34 may have exterior surfaces that generally include and define a pressure side 42 and a suction side 44 extending between a leading edge 46 and a trailing edge 48. Further, bucket assembly 34 may extend between a tip 52 and a root 54. The tip 52 may be, for example, a radially outward portion of the airfoil 34. The root 54 may be a radially inward portion of the shank 32 or dovetail 38.

A bucket assembly 30 according to the present disclosure further includes one or more cooling circuits defined therein. A cooling circuit may generally extend through the airfoil 34 and/or the shank 32. Cooling fluid (typically air or another suitable gas) may be flowed through the cooling circuits to cool the bucket assembly 30, and particularly the airfoil 34. For example, a bucket assembly 30 may include a main cooling circuit 60. The main cooling circuit 60 may be defined in the airfoil 34 and the shank 32. For example, the main cooling circuit 60 may extend through the shank 32 to the root 54, and may further extend from the root 54 through the shank 32 and into the airfoil 34.

As shown, the main cooling circuit 60 includes various cooling passages. In particular, a main cooling circuit 60 according to the present disclosure includes, such as consists of, seven cooling passages, including a first cooling passage 61, second cooling passage 62, third cooling passage 63, fourth cooling passage 64, fifth cooling passage 65, sixth cooling passage 66, and seventh cooling passage 67. Each cooling passage may extend generally radially through the bucket assembly 30. Each cooling passage may be connected to and thus in fluid communication with adjacent cooling passages. For example, the first cooling passage 61 may be in fluid communication with the second cooling passage 62, which in turn may be in fluid communication with the third cooling passage 63, etc. As soon, the cooling passages may be aligned in a row between the leading edge 46 and the trailing edge 48, and may thus be a generally chord-wise row. The cooling passages may be aligned sequentially, with the first cooling passage 61 positioned relatively closest to the trailing edge 48 and the seventh cooling passage 67 relatively closest to the leading edge 46. Cooling fluid may flow through each cooling passage in the main cooling circuit 60. Further, the connected cooling passages may have a generally serpentine pattern, such that the direction of flow through the cooling passages may alternate. For example, the general direction of flow in the first, third, fifth, and seventh cooling passages 61, 63, 65 and 67 may be in a generally radially outward direction towards the tip 52, and the general direction of flow in the second, fourth, and sixth cooling passages 62, 64, and 66 may be in a generally radially inward direction towards the root 54.

Each cooling passage of the main cooling circuit 60 may be defined at least partially in the airfoil 34 and, optionally, the shank 32. One or more cooling passage may additionally include one or more inlet portions, through which cooling fluid is provided to the main cooling circuit 60. For example, as shown, the first cooling passage 61 may include a first inlet portion 68 and a second inlet portion 69 defined in the shank 32 and extending to the root 54. The inlet portions 68, 69 may merge, such as in the shank 32 as shown, to form a singular first cooling passage 61.

The bucket assembly 30 may additionally include other various cooling circuits. For example, the bucket assembly 30 may include a forward cooling circuit 70. The forward cooling circuit 70 may be defined in the airfoil 34 and shank 32, and may extend from the root 54, as shown. Further, the forward cooling circuit 70 may be positioned generally chord-wise adjacent to the leading edge 46, such as between the leading edge 46 and the main cooling circuit 60. The forward cooling circuit 70 may include any suitable number of cooling passages, such as in exemplary embodiments a first cooling passage 71 and a second cooling passage 72.

The bucket assembly 30 may additionally or alternatively include an aft cooling circuit 80. The aft cooling circuit 80 may be defined in the airfoil 34 and shank 32, and may extend from the root 54, as shown. Further, the aft cooling circuit 80 may be positioned generally chord-wise adjacent to the trailing edge 48, such as between the trailing edge 48 and the main cooling circuit 60. The aft cooling circuit 80 may include any suitable number of cooling passages, such as in exemplary embodiments a first cooling passage 81.

Additionally, exhaust passages 90 may be defined in the airfoil 34. Each exhaust passage 90 may be connected to and thus in fluid communication with a passage of a cooling circuit, such as main cooling circuit 60, forward cooling circuit 70, or aft cooling circuit 80 as shown. The exhaust passages 90 may be provided for flowing the cooling fluid therethrough from the cooling circuits and exhausting the cooling fluid from the bucket assembly 30. In particular, exhaust passages 90 may be defined in the airfoil 34 and in fluid communication with the seventh passage 67 as shown, to exhaust cooling flow from the main cooling circuit 60. In some embodiments, the exhaust passages 90 may be, for example, oriented such that the exhausted cooling fluid provides film cooling of the bucket assembly 30.

Returning now to the main cooling circuit 60, such circuit 60 includes various features and characteristics that advantageously improve cooling of the bucket assembly 30. For example, as discussed above, the main cooling circuit 60 has seven cooling passages. This is an increase in the typical number of cooling passages included in previously known bucket assemblies. By increasing the number of cooling passages, the overall weight of the bucket assembly 30 and thickness of the walls and ribs of the airfoil 34 can be decreased. Further, however, the Mach number of the cooling flow in the cooling passages can advantageously be increased, leading to decreased coriolis effects in the cooling passages, which can thus provide more efficient and evenly distributed cooling of the bucket assembly 30 by the cooling passages. For example, the present inventors have discovered that cooling is improved in a bucket assembly by reducing the rotation number of the cooling flow in the cooling passages to less than or equal to approximately 0.4. The rotation number is a non-dimensional number that is inversely related to the Coriolis effect, and can be calculated based on the equation:

Ro=ω*b/(W/(ρA))

wherein Ro=rotation number (non-dimensional), ω=rotational velocity, b=passage cross-sectional length (as opposed to cross-sectional width a, see FIG. 5), W=cooling fluid mass flow rate, ρ=cooling fluid density, and A=cooling passage cross-sectional area (for example, a*b for a square or rectangular cooling passage cross-section). The design of the present main cooling circuit 60 according to the present disclosure thus provides a cooling flow with a maximum rotation number in each of the seven cooling passages 61, 62, 63, 64, 65, 66, 67 of less than or equal to approximately 0.4, such as in some embodiments less than or equal to approximately 0.35, such as in some embodiments between approximately 0.01 and approximately 0.4, such as in some embodiments between approximately 0.01 and approximately 0.35.

The present inventors have additionally discovered that further additional design characteristics of the present main cooling circuit 60 improve bucket assembly 30 cooling. For example, the present inventors have reduced the cross-sectional area of the first passage 61 of the main cooling circuit 60 in the airfoil 34 relative to the cross-sectional areas of the remaining passages 62, 63, 64, 65, 66, 67 in the airfoil 34. Cross-sectional area may be calculated in the view shown in FIG. 5 at any suitable location on the airfoil 34. The maximum cross-sectional area in the airfoil 34 of the first passage 61 may thus be in a range between approximately 10% and approximately 20% less than a maximum cross-sectional area in the airfoil 34 of any other passage 62, 63, 64, 65, 66, 67. Such reduction in the first passage 61 relative to the remaining passages 62, 63, 64, 65, 66, 67 further decreases the coriolis effect in the first passage 61, which is a location where the coriolis effect may formerly have been relatively more pronounced.

The present main cooling circuit 60 design additionally provides other various advantages. For example, cooling in the various turn regions wherein cooling flow is turned between adjacent cooling passages is improved due to the increased cooling flow Mach numbers when the cooling flow is entering the turn regions. Thus, the present bucket assembly 30 and main cooling circuit 60 provides a novel, advantageous solution to a bucket assembly 30 cooling problem recognized by the present inventors.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A bucket assembly, comprising: a shank; an airfoil positioned radially outward of the shank; a main cooling circuit defined in the airfoil and the shank, the main cooling circuit comprising seven passages, each of the seven passages fluidly connected with an adjacent one of the seven passages, wherein a maximum rotation number in each of the seven passages is less than or equal to approximately 0.4.
 2. The bucket assembly of claim 1, wherein the rotation number in each of the seven passages is in a range between approximately 0.01 and approximately 0.35.
 3. The bucket assembly of claim 1, wherein a first passage of the seven passages has a maximum cross-sectional area in the airfoil that is in a range between approximately 10% and approximately 20% less than a maximum cross-sectional area in the airfoil of another passage of the seven passages.
 4. The bucket assembly of claim 1, further comprising an exhaust passage defined in the airfoil and in fluid communication with a seventh passage of the seven passages.
 5. The bucket assembly of claim 1, further comprising a forward cooling circuit and an aft cooling circuit are each defined in the airfoil and the shank.
 6. The bucket assembly of claim 1, wherein the main cooling circuit consists of seven passages.
 7. The bucket assembly of claim 1, further comprising a platform positioned radially between the shank and the airfoil.
 8. The bucket assembly of claim 1, wherein the airfoil has exterior surfaces defining a pressure side and a suction side extending between a leading edge and a trailing edge.
 9. The bucket assembly of claim 1, further comprising a dovetail.
 10. The bucket assembly of claim 1, wherein the dovetail defines a root, and wherein the main cooling circuit extends to the root.
 11. A turbomachine, comprising: an inlet section; an exhaust section; a compressor section; a combustor section; and a turbine section, the turbine section comprising a plurality of bucket assemblies, each of the plurality of bucket assemblies comprising: a shank; an airfoil positioned radially outward of the shank; a main cooling circuit defined in the airfoil and the shank, the main cooling circuit comprising seven passages, each of the seven passages fluidly connected with an adjacent one of the seven passages, wherein a maximum rotation number in each of the seven passages is less than or equal to approximately 0.4.
 12. The turbomachine of claim 11, wherein the rotation number in each of the seven passages is in a range between approximately 0.01 and approximately 0.35.
 13. The turbomachine of claim 11, wherein a first passage of the seven passages has a maximum cross-sectional area in the airfoil that is in a range between approximately 10% and approximately 20% less than a maximum cross-sectional area in the airfoil of another passage of the seven passages.
 14. The turbomachine of claim 11, further comprising an exhaust passage defined in the airfoil and in fluid communication with a seventh passage of the seven passages.
 15. The turbomachine of claim 11, further comprising a forward cooling circuit and an aft cooling circuit are each defined in the airfoil and the shank.
 16. The turbomachine of claim 11, wherein the main cooling circuit consists of seven passages.
 17. The turbomachine of claim 11, further comprising a platform positioned radially between the shank and the airfoil.
 18. The turbomachine of claim 11, wherein the airfoil has exterior surfaces defining a pressure side and a suction side extending between a leading edge and a trailing edge.
 19. The turbomachine of claim 11, further comprising a dovetail.
 20. The turbomachine of claim 11, wherein the dovetail defines a root, and wherein the main cooling circuit extends to the root. 